Regulated recruitment of DC-SIGN to cell-cell contact regions during zymosan-induced human dendritic cell aggregation

Co-cultivation effects of Lactobacillus helveticus SNA12 and Kluveromyces marxiensis GY1 on the probiotic properties, flavor, and digestion in fermented milk

This study aimed to evaluate inoculating the lactic acid bacteria Lactobacillus helveticus SNA12 and the yeast Kluyveromyces marxiensis GY1 as starter cultures on milk fermentation. In this study, the probiotic properties of L. helveticus SNA12, K. marxiensis GY1 and co-culture of these two strains (L. helveticus SNA12-K. marxiensis GY1) were investigated, and the results showed that K. marxiensis GY1 had better gastrointestinal tolerance, aggregation, and cell adhesion properties than L. helveticus SNA12. After the co-cultivation of two strains, the presence of K. marxiensis GY1 significantly increased the gastrointestinal tolerance, aggregation, and adhesion characteristics of L. helveticus SNA12. In order to investigate the flavor changes, digestive characteristics, and antioxidant properties following co-cultivation fermentation, the optimal fermentation ratio of 8 %-2% (v/v) and fermentation temperature (37 °C) of L. helveticus SNA12-K. marxiensis GY1 were determined. The results of the electronic nose and electronic tongue showed that L. helveticus SNA12-K. marxiensis GY1 could increase the aroma components of fermented milk, such as terpenes and aromatic substances. Meanwhile, dynamic in vitro rat stomach-duodenum model was used to analyse the changes in the digestion of proteins and peptides (<10 kDa), and the results indicated that co-cultivation fermented milk could be digested faster compared to a single fermentation. Furthermore, the antioxidant capacity of co-cultivation fermented milk was higher than that of single fermentation.

Dectin-1-Mediated DC-SIGN Recruitment to Candida albicans Contact Sites

At host-pathogen contact sites with Candida albicans, Dectin-1 activates pro-inflammatory signaling, while DC-SIGN promotes adhesion to the fungal surface. We observed that Dectin-1 and DC-SIGN collaborate to enhance capture/retention of C. albicans under fluid shear culture conditions. Therefore, we devised a cellular model system wherein we could investigate the interaction between these two receptors during the earliest stages of host-pathogen interaction. In cells expressing both receptors, DC-SIGN was quickly recruited to contact sites (103.15% increase) but Dectin-1 did not similarly accumulate. Once inside the contact site, FRAP studies revealed a strong reduction in lateral mobility of DC-SIGN (but not Dectin-1), consistent with DC-SIGN engaging in multivalent adhesive binding interactions with cell wall mannoprotein ligands. Interestingly, in the absence of Dectin-1 co-expression, DC-SIGN recruitment to the contact was much poorer-only 35.04%. These data suggested that Dectin-1 promotes the active recruitment of DC-SIGN to the contact site. We proposed that Dectin-1 signaling activates the RHOA pathway, leading to actomyosin contractility that promotes DC-SIGN recruitment, perhaps via the formation of a centripetal actomyosin flow (AMF) directed into the contact site. Indeed, RHOA pathway inhibitors significantly reduced Dectin-1-associated DC-SIGN recruitment to the contact site. We used agent-based modeling to predict DC-SIGN transport kinetics with ("Directed + Brownian") and without ("Brownian") the hypothesized actomyosin flow-mediated transport. The Directed + Brownian transport model predicted a DC-SIGN contact site recruitment (106.64%), similar to that we observed experimentally under receptor co-expression. Brownian diffusive transport alone predicted contact site DC-SIGN recruitment of only 55.60%. However, this value was similar to experimentally observed DC-SIGN recruitment in cells without Dectin-1 or expressing Dectin-1 but treated with RHOA inhibitor, suggesting that it accurately predicted DC-SIGN recruitment when a contact site AMF would not be generated. TIRF microscopy of nascent cell contacts on glucan-coated glass revealed Dectin-1-dependent DC-SIGN and F-actin (LifeAct) recruitment kinetics to early stage contact site membranes. DC-SIGN entry followed F-actin with a temporal lag of 8.35 ± 4.57 s, but this correlation was disrupted by treatment with RHOA inhibitor. Thus, computational and experimental evidence provides support for the existence of a Dectin-1/RHOA-dependent AMF that produces a force to drive DC-SIGN recruitment to pathogen contact sites, resulting in improved pathogen capture and retention by immunocytes. These data suggest that the rapid collaborative response of Dectin-1 and DC-SIGN in early contact sties might be important for the efficient acquisition of yeast under flow conditions, such as those that prevail in circulation or mucocutaneous sites of infection.

Intracellular Galectin-9 Controls Dendritic Cell Function by Maintaining Plasma Membrane Rigidity

Endogenous extracellular Galectins constitute a novel mechanism of membrane protein organization at the cell surface. Although Galectins are also highly expressed intracellularly, their cytosolic functions are poorly understood. Here, we investigated the role of Galectin-9 in dendritic cell (DC) surface organization and function. By combining functional, super-resolution and atomic force microscopy experiments to analyze membrane stiffness, we identified intracellular Galectin-9 to be indispensable for plasma membrane integrity and structure in DCs. Galectin-9 knockdown studies revealed intracellular Galectin-9 to directly control cortical membrane structure by modulating Rac1 activity, providing the underlying mechanism of Galectin-9-dependent actin cytoskeleton organization. Consequent to its role in maintaining plasma membrane structure, phagocytosis studies revealed that Galectin-9 was essential for C-type-lectin receptor-mediated pathogen uptake by DCs. This was confirmed by the impaired phagocytic capacity of Galectin-9-null murine DCs. Together, this study demonstrates a novel role for intracellular Galectin-9 in modulating DC function, which may be evolutionarily conserved.

West Nile virus T-cell ligand sequences shared with other flaviviruses: a multitude of variant sequences as potential altered peptide ligands

Phylogenetic relatedness and cocirculation of several major human pathogen flaviviruses are recognized as a possible cause of deleterious immune responses to mixed infection or immunization and call for a greater understanding of the inter-Flavivirus protein homologies. This study focused on the identification of human leukocyte antigen (HLA)-restricted West Nile virus (WNV) T-cell ligands and characterization of their distribution in reported sequence data of WNV and other flaviviruses. H-2-deficient mice transgenic for either A2, A24, B7, DR2, DR3, or DR4 HLA alleles were immunized with overlapping peptides of the WNV proteome, and peptide-specific T-cell activation was measured by gamma interferon (IFN-γ) enzyme-linked immunosorbent spot (ELISpot) assays. Approximately 30% (137) of the WNV proteome peptides were identified as HLA-restricted T-cell ligands. The majority of these ligands were conserved in ∼≥88% of analyzed WNV sequences. Notably, only 51 were WNV specific, and the remaining 86, chiefly of E, NS3, and NS5, shared an identity of nine or more consecutive amino acids with sequences of 64 other flaviviruses, including several major human pathogens. Many of the shared ligands had an incidence of >50% in the analyzed sequences of one or more of six major flaviviruses. The multitude of WNV sequences shared with other flaviviruses as interspecies variants highlights the possible hazard of defective T-cell activation by altered peptide ligands in the event of dual exposure to WNV and other flaviviruses, by either infection or immunization. The data suggest the possible preferred use of sequences that are pathogen specific with minimum interspecies sequence homology for the design of Flavivirus vaccines.

GM-CSF plays a key role in zymosan-stimulated human dendritic cells for activation of Th1 and Th17 cells

In this study, we compared the effects of zymosan and LPS on human monocyte-derived dendritic cells. The specific effects of zymosan on the expression of several key cytokines, including granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukins (IL-1α, IL-1β and IL-12 p70) were quite distinct from the effects of LPS. Unlike activation with LPS, DCs activated by zymosan expressed little or no IL-12 p70 due to lack of expression of the p35 subunit. However, treatment with zymosan resulted in a substantial increase in Th1 and Th17 cell-polarizing capacity of DCs. Furthermore, the GM-CSF secreted by zymosan-activated DCs enhanced IL-23 production, resulting in activation of a Th17 response. GM-CSF and IL-27, rather than IL-12 p70, were both major direct contributors to the activation of a Th1 response. This signaling mechanism is distinct and yet complementary to LPS-mediated T-cell activation. We suggest that this novel zymosan-induced GM-CSF-mediated signaling network may play a key role in regulating specific immune cell type activities.

Eicosanoids in the innate immune response: TLR and non-TLR routes

The variable array of pattern receptor expression in different cells of the innate immune system explains the induction of distinct patterns of arachidonic acid (AA) metabolism. Peptidoglycan and mannan were strong stimuli in neutrophils, whereas the fungal extract zymosan was the most potent stimulus in monocyte-derived dendritic cells since it induced the production of PGE₂, PGD₂, and several cytokines including a robust IL-10 response. Zymosan activated κB-binding activity, but inhibition of NF-κB was associated with enhanced IL-10 production. In contrast, treatments acting on CREB (CRE binding protein), including PGE₂, showed a direct correlation between CREB activation and IL-10 production. Therefore, in dendritic cells zymosan induces il10 transcription by a CRE-dependent mechanism that involves autocrine secretion of PGE₂, thus unraveling a functional cooperation between eicosanoid production and cytokine production.

Candida albicans beta-glucan exposure is controlled by the fungal CEK1-mediated mitogen-activated protein kinase pathway that modulates immune responses triggered through dectin-1

Innate immunity to Candida albicans depends upon the recognition of molecular patterns on the fungal cell wall. However, the masking of major components such as beta-glucan seems to be a mechanism that fungi have evolved to avoid immune cell recognition through the dectin-1 receptor. Although the role of C. albicans mitogen-activated protein kinase (MAPK) pathways as virulence determinants has been established previously with animal models, the mechanism involved in this behavior is largely unknown. In this study we demonstrate that a disruption of the C. albicans extracellular signal-regulated kinase (ERK)-like 1 (CEK1)-mediated MAPK pathway causes enhanced cell wall beta-glucan exposure, triggering immune responses more efficiently than the wild type, as measured by dectin-1-mediated specific binding and human dendritic cell (hDC)- and macrophage-mediated phagocytosis, killing, and activation of intracellular signaling pathways. At the molecular level, the disruption of CEK1 resulted in altered spleen tyrosine kinase (Syk), Raf-1, and ERK1/2 activations together with IkappaB degradation on hDCs and increased dectin-1-dependent activator protein 1 (AP-1) activation on transfected cells. In addition, concurring with these altered pathways, we detected increased reactive oxygen species production and cytokine secretion. In conclusion, the CEK1-mediated MAPK pathway is involved in beta-glucan exposure in a fungal pathogen, hence influencing dectin-1-dependent immune cell recognition, thus establishing this fungal intracellular signaling route as a promising novel therapeutic target.

The induction of IL-10 by zymosan in dendritic cells depends on CREB activation by the coactivators CREB-binding protein and TORC2 and autocrine PGE2

Stimulation of human monocyte-derived dendritic cells with the yeast extract zymosan is characterized by a predominant production of IL-10 and a strong induction of cyclooxygenase-2, but the molecular mechanisms underlying this response are only partially understood. To address this issue, the activation of transcription factors that may bind to the il10 proximal promoter was studied. Binding activity to Sp1, Sp3, NF-Y, and cAMP response element (CRE) sites was detected in the nuclear extracts of dendritic cells; however these binding activities were not influenced by zymosan. No binding activity to Stat1, Stat3, and c/EBP sites was detected. Notably, zymosan activated kappaB-binding activity, but inhibition of NF-kappaB was associated with enhanced IL-10 production. In sharp contrast, treatments acting on CREB (CRE binding protein), including 8-Br-cAMP, PGE(2), and inhibitors of PKA, COX, and glycogen-synthase kinase-3beta showed a direct correlation between CREB activation and IL-10 production. Zymosan induced binding of both P-CREB and CREB-binding protein (CBP) to the il10 promoter as judged from chromatin immunoprecipitation assays, whereas negative results were obtained with Ab reactive to Sp1, Sp3, c-Maf, and NF-Y. Zymosan also induced nuclear translocation of the CREB coactivator transducer of regulated CREB activity 2 (TORC2) and interaction of TORC2 with P-CREB coincidental with the association of CREB to the il10 promoter. Altogether, our data show that zymosan induces il10 transcription by a CRE-dependent mechanism that involves autocrine secretion of PGE(2) and a network of interactions of PKA, MAP/ERK, glycogen-synthase kinase-3beta, and calcineurin, which regulate CREB transcriptional activity by binding the coactivators CBP and TORC2 and inhibiting CBP interaction with other transcription factors.

Immunomodulatory effects of beta-glucans on porcine alveolar macrophages and bone marrow haematopoietic cell-derived dendritic cells

The immunopharmacological activities of beta-glucans with a backbone of beta-1,3/beta-1,6-linkages associated with anti-tumor, anti-viral, bacterial and fungal infections have been well documented. Dectin-1, a specific pattern recognition receptor for beta-1,3/beta-1,6-glucans, is expressed mainly on phagocytes, especially macrophages and dendritic cells (DCs). In this study, the encoding nucleotide for the carbohydrate-recognition domain (CRD) of porcine dectin-1 was sequenced for the first time, and the immunomodulatory functions of a synthetic particulate beta-glucan (p-beta-glucan) were examined. Results showed that p-beta-glucan significantly enhanced cell activity and phagocytosis in porcine alveolar macrophages (AMs), immature DCs (imDCs) and mature DCs (mDCs), in a similar way to zymosan. Zymosan enhanced dectin-1/TLR2/TLR4 expression and TNF-alpha/IL-10 production in all of three types of cell, whereas p-beta-glucan increased dectin-1/TLR4 and TNF-alpha/IL-12 production in AMs but inhibited IL-10 in mDCs. These results indicate that the complex collaborating interactions between dectin-1 and TLRs in the recognition of beta-1,3/beta-1,6-glucans with different structural features may direct different cellular responses.

Costimulation of dectin-1 and DC-SIGN triggers the arachidonic acid cascade in human monocyte-derived dendritic cells

Inflammatory mediators derived from arachidonic acid (AA) alter the function of dendritic cells (DC), but data regarding their biosynthesis resulting from stimulation of opsonic and nonopsonic receptors are scarce. To address this issue, the production of eicosanoids by human monocyte-derived DC stimulated via receptors involved in Ag recognition was assessed. Activation of FcgammaR induced AA release, short-term, low-grade PG biosynthesis, and IL-10 production, whereas zymosan, which contains ligands of both the mannose receptor and the human beta-glucan receptor dectin-1, induced a wider set of responses including cyclooxygenase 2 induction and biosynthesis of leukotriene C(4) and IL-12p70. The cytosolic phospholipase A(2) inhibitor pyrrolidine 1 completely inhibited AA release stimulated via all receptors, whereas the spleen tyrosine kinase (Syk) inhibitors piceatannol and R406 fully blocked AA release in response to immune complexes, but only partially blocked the effect of zymosan. Furthermore, anti-dectin-1 mAb partially inhibited the response to zymosan, and this inhibition was enhanced by mAb against DC-specific ICAM-3-grabbing nonintegrin (SIGN). Immunoprecipitation of DC lysates showed coimmunoprecipitation of DC-SIGN and dectin-1, which was confirmed using Myc-dectin-1 and DC-SIGN constructs in HEK293 cells. These data reveal a robust metabolism of AA in human DC stimulated through both opsonic and nonopsonic receptors. The FcgammaR route depends on the ITAM/Syk/cytosolic phospholipase A(2) axis, whereas the response to zymosan involves the interaction with the C-type lectin receptors dectin-1 and DC-SIGN. These findings help explain the distinct functional properties of DC matured by immune complexes vs those matured by beta-glucans.

Structural requirements for multimerization of the pathogen receptor dendritic cell-specific ICAM3-grabbing non-integrin (CD209) on the cell surface

The myeloid C-type lectin dendritic cell-specific ICAM3-grabbing non-integrin (DC-SIGN, CD209) recognizes oligosaccharide ligands on clinically relevant pathogens (HIV, Mycobacterium, and Aspergillus). Alternative splicing and genomic polymorphism generate DC-SIGN mRNA variants, which have been detected at sites of pathogen entrance and transmission. We present evidence that DC-SIGN neck variants are expressed on dendritic and myeloid cells at the RNA and protein levels. Structural analysis revealed that multimerization of DC-SIGN within a cellular context depends on the lectin domain and the number and arrangement of the repeats within the neck region, whose glycosylation negatively affects oligomer formation. Naturally occurring DC-SIGN neck variants differ in multimerization competence in the cell membrane, exhibit altered sugar binding ability, and retain pathogen-interacting capacity, implying that pathogen-induced cluster formation predominates over the basal multimerization capability. Analysis of DC-SIGN neck polymorphisms indicated that the number of allelic variants is higher than previously thought and that multimerization of the prototypic molecule is modulated in the presence of allelic variants with a different neck structure. Our results demonstrate that the presence of allelic variants or a high level of expression of neck domain splicing isoforms might influence the presence and stability of DC-SIGN multimers on the cell surface, thus providing a molecular explanation for the correlation between DC-SIGN polymorphisms and altered susceptibility to HIV-1 and other pathogens.

Human seminal plasma abrogates the capture and transmission of human immunodeficiency virus type 1 to CD4+ T cells mediated by DC-SIGN

Dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN) is expressed by dendritic cells (DCs) at mucosal surfaces and appears to play an important role in the dissemination of human immunodeficiency virus type 1 (HIV-1) infection. DC-SIGN binds HIV-1 gp120 and efficiently transmits the virus to T CD4(+) cells, which become the center of viral replication. Semen represents the main vector for HIV-1 dissemination worldwide. In the present study we show that human seminal plasma (SP), even when used at very high dilutions (1:10(4) to 1:10(5)), markedly inhibits the capture and transmission of HIV-1 to T CD4(+) cells mediated by both DCs and B-THP-1-DC-SIGN cells. In contrast, SP does not inhibit the capture of HIV-1 by DC-SIGN-negative target cells, such as the T-cell line SupT-1, monocytes, and activated peripheral blood mononuclear cells. The SP inhibitor has a high molecular mass (>100 kDa) and directly interacts with DC-SIGN-positive target cells but not with HIV-1. Moreover, the inhibitor binds to concanavalin A, suggesting that it contains high-mannose N-linked carbohydrates. Of note, using biotin-labeled SP we found that the binding of SP components to DCs was abrogated by mannan, while their interaction with B-THP-1 cells was almost completely dependent on the expression of DC-SIGN. Since epithelium integrity is often compromised after vaginal or anal intercourse, as well as in the presence of ulcerative-sexually transmitted diseases, our results support the notion that components of the SP might be able to access to the subepithelium, inhibiting the recognition of HIV-1 gp120 by DC-SIGN-positive DCs.

Langerhans Cell Receptors

Langerhans cells (LC) are a subtype of dendritic cells, which reside in the epidermis. LCs are antigen-presenting cells that originate in bone marrow and enter the epidermis through blood vessels. LCs exhibit a variety of antigen receptors that are able to respond to a wide range of antigens. Within the last two decades, these receptors have been the subject of considerable research. This article focuses on the rapidly growing body of knowledge with respect to the functions of LC receptors.

hDectin-1 is involved in uptake and cross-presentation of cellular antigens

Human Dectin-1 (hDectin-1) is a member of the C-type lectin-like receptor family that was shown to be the major receptor for fungal beta-glucans and to play an important role in the cellular responses mediated by these carbohydrates. In this study, we demonstrate that hDectin-1 is involved in the uptake and cross-presentation of cellular antigens. Furthermore, activation of monocyte-derived dendritic cells (MDCs) with toll-like receptor 3 (TLR3) ligand but not with TLR2 ligand or TLR7 ligand resulted in down-regulation of hDectin-1 expression and reduced phagocytosis of apoptotic tumor cells as well as presentation of pp65-derived T-cell epitopes upon engulfment of cytomegalovirus (CMV)-infected human foreskin fibroblasts.

NADPH oxidase of human dendritic cells: role in Candida albicans killing and regulation by interferons, dectin-1 and CD206

Human monocyte-derived DC express the enzyme NADPH oxidase, responsible for ROS production. We show that Candida albicans did not activate NADPH oxidase in DC, and was poorly killed by these cells. However, Candida-killing activity increased upon DC stimulation with the NADPH oxidase activator PMA and was further enhanced by DC treatment with IFN-alpha or IFN-gamma. This fungicidal activity took place at high DC-to-Candida ratio, but decreased at low DC-to-yeast ratio, when Candida inhibited the NADPH oxidase by contrasting the assembly of the enzyme on DC plasma membrane. The NADPH oxidase inhibitor diphenyliodonium chloride abrogated the PMA-dependent DC candidacidal capacity. Engagement of beta-glucan receptor dectin-1 induced NADPH oxidase activation in DC that was depressed by mannose-binding receptor CD206 co-stimulation. Candida was internalized by DC through mannose-binding receptors, but not through dectin-1, thus explaining why Candida did not elicit NADPH oxidase activity. Our results indicate that NADPH oxidase is involved in DC Candida-killing activity, which is increased by IFN. However, Candida escapes the oxidative damage by inhibiting NADPH oxidase and by entering DC through receptors not involved in NADPH oxidase activation.

The DC-SIGN–related lectin LSECtin mediates antigen capture and pathogen binding by human myeloid cells

Liver and lymph node sinusoidal endothelial cell C-type lectin (LSECtin [CLEC4G]) is a C-type lectin encoded within the liver/lymph node–specific intercellular adhesion molecule-3–grabbing nonintegrin (L-SIGN)/dendritic cell–specific intercellular adhesion molecule-3–grabbing nonintegrin (DC-SIGN)/CD23 gene cluster. LSECtin expression has been previously described as restricted to sinusoidal endothelial cells of the liver and lymph node. We now report LSECtin expression in human peripheral blood and thymic dendritic cells isolated ex vivo. LSECtin is also detected in monocyte-derived macrophages and dendritic cells at the RNA and protein level. In vitro, interleukin-4 (IL-4) induces the expression of 3 LSECtin alternatively spliced isoforms, including a potentially soluble form (Δ2 isoform) and a shorter version of the prototypic molecule (Δ3/4 isoform). LSECtin functions as a pathogen receptor, because its expression confers Ebola virus–binding capacity to leukemic cells. Sugar-binding studies indicate that LSECtin specifically recognizes N-acetyl-glucosamine, whereas no LSECtin binding to Mannan- or N-acetyl-galactosamine–containing matrices are observed. Antibody or ligand-mediated engagement triggers a rapid internalization of LSECtin,which is dependent on tyrosine and diglutamic-containing motifs within the cytoplasmic tail. Therefore, LSECtin is a pathogen-associated molecular pattern receptor in human myeloid cells. In addition, our results suggest that LSECtin participates in antigen uptake and internalization, and might be a suitable target molecule in vaccination strategies.

AM3 modulates dendritic cell pathogen recognition capabilities by targeting DC-SIGN

AM3 (Inmunoferon) is an orally effective immunomodulator that influences the regulatory and effector functions of the immune system whose molecular mechanisms of action are mostly unknown. We hypothesized that the polysaccharide moiety of AM3 (IF-S) might affect immune responses by modulating the lectin-dependent pathogen recognition abilities of human dendritic cells. IF-S inhibited binding of viral, fungal, and parasite pathogens by human monocyte-derived dendritic cells in a dose-dependent manner. IF-S specifically impaired the pathogen recognition capabilities of DC-SIGN, as it reduced the attachment of Candida, Aspergillus, and Leishmania to DC-SIGN transfectants. IF-S also inhibited the interaction of DC-SIGN with both its cellular counterreceptor (intercellular adhesion molecule 3) and the human immunodeficiency virus (HIV) type 1 gp120 protein and blocked the DC-SIGN-dependent capture of HIV virions and the HIV trans-infection capability of DC-SIGN transfectants. IF-S promoted DC-SIGN internalization in DCs without affecting mannose receptor expression, and (1)D saturation transfer difference nuclear magnetic resonance demonstrated that IF-S directly interacts with DC-SIGN on the cell surface. Therefore, the polysaccharide moiety of AM3 directly influences pathogen recognition by dendritic cells by interacting with DC-SIGN. Our results indicate that DC-SIGN is the target for an immunomodulator and imply that the adjuvant and immunomodulatory actions of AM3 are mediated, at least in part, by alteration of the DC-SIGN functional activities.

Medicinal importance of fungal beta-(1-->3), (1-->6)-glucans

Non-cellulosic beta-glucans are now recognized as potent immunological activators, and some are used clinically in China and Japan. These beta-glucans consist of a backbone of glucose residues linked by beta-(1-->3)-glycosidic bonds, often with attached side-chain glucose residues joined by beta-(1-->6) linkages. The frequency of branching varies. The literature suggests beta-glucans are effective in treating diseases like cancer, a range of microbial infections, hypercholesterolaemia, and diabetes. Their mechanisms of action involve them being recognized as non-self molecules, so the immune system is stimulated by their presence. Several receptors have been identified, which include: dectin-1, located on macrophages, which mediates beta-glucan activation of phagocytosis and production of cytokines, a response co-ordinated by the toll-like receptor-2. Activated complement receptors on natural killer cells, neutrophils, and lymphocytes, may also be associated with tumour cytotoxicity. Two other receptors, scavenger and lactosylceramide, bind beta-glucans and mediate a series of signal pathways leading to immunological activation. Structurally different beta-glucans appear to have different affinities toward these receptors and thus generate markedly different host responses. However, the published data are not always easy to interpret as many of the earlier studies used crude beta-glucan preparations with, for the most part, unknown chemical structures. Careful choice of beta-glucan products is essential if their benefits are to be optimized, and a better understanding of how beta-glucans bind to receptors should enable more efficient use of their biological activities.

Phagocytosis induces lysosome remodeling and regulated presentation of particulate antigens by activated dendritic cells

Immunization with particulate Ag effectively induces antitumor and antiviral T cell-mediated immunity. Immature dendritic cells (DCs) efficiently internalize, process, and present a variety of particulate Ags; however, previously published data suggest that both the uptake of soluble Ag through micropinocytosis, and phagocytosis of particulates are significantly curtailed in activated DC populations. In this study, we demonstrate that although macropinocytosis of soluble Ag is diminished following DC activation, subsets of DCs in activated DC populations retain the ability to actively phagocytose particulate Ags. Live cell imaging of activated DCs reveals that phagocytosis of particulates can result in cytoskeletal remodeling and perinuclear lysosome cluster disruption in a time-dependent manner. Interestingly, our results suggest that in activated DC populations, presentation of phagocytosed particulate Ags is dependent on the nature of the activation signal. These results provide direct evidence of functional heterogeneity in DC populations and contribute to the development of particle-based immunization strategies.